File



J. F. CRATER Sept! 17, 1940.

FILE

Filed May 17, 1939 INVENTOR. JOHN F CRATER 11am 5 v w I ATTORNEY.

Patented Sept. 17, 1940 FILE John Floyd Crater, Cleveland, Ohio, assignor to Cleveland File Company, Cleveland, Ohio, a

corporation of Ohio Application May 17, 1939, Serial No. 274,244

4 Claims.

This invention relates to a file and is more particularly directed to a file which may be curved asdesired such that its cutting surface does not lie in a plane.

Curved files are well known but insofar as I am aware these have been of two general types. One has consisted of a flexible and thin toothed member too thin and weak to be self supporting, backed up by a reinforcing member of the desired curvature. The two parts were secured together, generally by screws passing therethrough. These screw holes frequently had rough edges and were liable to scratch the work and thus mar the finish otherwise secured. The other type was formed to a radius before hardening and then hardened. The file thus had a definite contour and being brittle, could not be formed to a different radius. Both of these types of files were adapted for use over only one curvature and this could not be varied unless the parts were changed. The cost of these files has been high. In the first place this was because of the parts required and time required in taking them apart and putting them together. In the second case the file could be used only on the convex side and this was a waste of half the file.

It has been the general object of my invention to overcome these previous objections in files and to provide a new and improved file which possesses new and marked characteristics which are of considerable commercial advantage. Another object of my invention has been to provide a file which may be bent without breakage and which will retain the position to which it is bent. Still another object of the invention has been to provide a file with very hard cutting teeth and a soft and ductile core to provide great strength and to resist breakage and which is of itself entirely self supporting.

In general, my file is composed of a hard wearresisting toothed outer portion and a ductile core portion. The teeth may be on one or more sides of the body as desired. The core is soft and susceptible of bending while the outer tooth portion is extremely hard to outwith little wear and to give long life to the teeth in use.

To the accomplishment of the foregoing and related ends, said invention, then, consists of the elements hereinafter fully described and particularly pointed out in the claims; the annexed drawing and the following description setting forth in detail certain structure embodying the invention, such disclosed elements constituting, however, but one of various structural forms in which the principle of the invention may be used.

In said annexed drawing: Fig. 1 is a plan view of my improved file;

Fig. 2 is a transverse View therethrough on the with the carbon content varying between 90 and 140 points. In most cases the carbon content will be between 110 and 115 points of carbon. This blank 5 is made up in the usual way into file form by forming the blank to the desired shape and chiseling teeth therein. It will be understood that the preferred form of file shown in the drawing may be modified without departing from the scope of the invention. The blank is of sufiicient size to be self supporting and is not backed up as are the old type of curved files.

Teeth, as indicated at 6, are cut in the two fiat faces, although for certain files more or less toothed portions may be provided.

The file is heat treated to provide hardened teeth and a soft core after it has been formed to the desired shape and after the teeth have been cut. This heat treatment may be effected in alternative ways, although the following is the preferred manner. A lead hardening bath is brought to a temperature of approximately 1350 F. and the files are immersed in the bath for approximately twelve minutes. At the end of this time they are removed and rapidly quenched in a brine solution. The heating temperature and the time for heating is sufficient to heat all points of the file above the critical hardening temperature. As the file is quenched, the teeth, because of their large surface exposure being on the exterior, are very rapidly cooled. The AR 32-l line of the iron carbon diagram is by this action decreased so far that the teeth become extremely hard, in some cases exceeding 58 on the Rockwell G. Scale. The heat content of the interior however, is such that this part of the file cools less rapidly with a consequent drawing of the temperature, resulting in a relatively ductile core or body portion.

A file constructed in accordance with the above teaching is possessed of a core 8 which is soft enough to allow appreciable bending before breakage takes place. The hard outer surface of the file however, being intensely brittle, will acquire slight checks l0 extending generally from the tooth roots inwardly to the inner boundary of the hardened zone. The heat treatment is such that a bond is maintained between the main tooth portion and the file core and thus there is no flaking off of the teeth.

As a file of this nature is bent, with the sub sequent tooth checking, certain improved characteristics appear in the wearing quality of the teeth. I attribute this to the fact that as the file is bent the teeth project out from the general file surface enough more than in the ordinary file to produce a more exposed tooth cutting edge and the checks enhance the amount the teeth can extend.

An alternative process for forming my improved file consists in heating for a period so short that the core is not brought to hardening temperature. The forming tool is immersed in a lead bath for a very short period of time, as a minute, at about 1400 F. and is then quenched in a brine solution. In this latter case, the core portion is not subjected to any appreciable hardening effect, and hence is not subject to any quenching action requiring a draw of the temper. The teeth, however, being exposed, rapidly absorb sufiicient heat to be raised above the critical temperature and thus in quenching are made intensely hard. The result is a file with characteristics equivalent to those made by the first method.

A file made as above described may be bent, as with a rawhide mallet, to any reasonable angle or radius suitable to the use of the particular workman. Similarly, the file is well adapted for draw filing since it can be bent to the exact radius of the work being done, as for instance, the portions of an automobile body which are soldered and are of considerable radius.

My improved file is well adapted for use as a combined scraper and file because of the curvature which may be applied to the file body, allowing ready use of the end during a scraping operation while still possessing the qualities of a file during a filing operation.

The file will leave a much finer finish and there will be no chatter in the teeth, due, I believe, to the pronounced tooth angle due to bending, and the aforementioned root checks formed when the outer tooth surface is ruptured. After the teeth on one side of the file are worn out, the file may be bent the opposite way and the teeth on that side used in exactly the same manner as the first set. In ordinary filing the life of a file may be considerably lengthened by slightly bending the file about a shorter radius as the teeth wear, thus allowing more of an individual tooth to protrude into work engaging relation with the work being filed.

Other forms may be employed embodying the features of my invention instead of the one herein explained, change being made in the form or construction, provided the elements stated by any of the following claims or the equivalent of such stated elements be employed.

I therefore particularly point out and distinctly claim as my invention: a

1. In a steel file, a series of cutting teeth provide small transverse checks in the region of the roots of said file teeth.

2. In a file formed of steel with a carbon content of approximately .90 to 1.40 percent, a series of cutting teeth formed in at least one face thereof, a relatively soft and ductile body portion 3 extending substantially throughout said file body and closely underlying said teeth and characterized by an ability to be bent and set through a substantial angle with respect to the general plane of the file, and a hard brittle tooth struc- 2" ture with a hard, brittle surface portion extending across the tooth roots, said hardbrittle portion characterized by a hardness sufiicient to abrade and a brittleness sufiicient to check upon appreciable bending to provide small transverse I checks in the region of the roots of said file teeth.

3. In a file formed of plain carbon steel, a series of cutting teeth formed in at least one face thereof, a relatively soft and ductile body portion extending substantially throughout said file body and closely underlying said teeth and characterized by an ability to be bent and set through a substantial angle with respect to the general plane of the file, and a hard brittle tooth structure with a similar shallow hardened portion underlying said teeth and interposed between the teeth and the core portion and characterized by a hardness suificient to abrade and a brittleness sufiicient to check upon appreciable bending.

4. In a file formed of plain carbon steel with a carbon content of approximately 1.10 to 1.15 percent, a series of cutting teeth formed in at least one face thereof, a relatively soft and ductile body portion extending substantially throughout said file body and closely underlying said teeth and characterized by an ability to be bent and set through a substantial angle with respect to the general plane of the file, and a hard brittle toothstructure with a similar shallow hardened por- 

